1. Field
This disclosure relates generally to semiconductors, and more specifically, to semiconductor devices with stressors.
2. Related Art
In the development integrated circuits, one of the improvements in performance has been the use of altering the strain in the channel of MOS transistors to increase carrier mobility. Electron mobility has been found to improve by providing tensile stress in the channel of N channel transistors, and hole mobility has been found to improve by providing compressive stress in the channel of P channel transistors. The mobility improvement is generally proportional to the stress in the channel. As long as the monocrystalline structure is maintained in the channel, more stress is better. Thus, there is generally an improvement if an increase in stress is provided for a given transistor. Improvement in overall integrated circuit performance can be achieved by improving the performance of either the P or N channel transistors while not degrading the other. This type of improvement can be sufficient for many applications and is likely to add less process complexity than attempting to provide both compressive stress for the P channel transistors and tensile stress for the N channel transistors.
Thus there is a need for achieving one or more of the above objectives while increasing stress.